1. Field of the Invention
Stick-form rigid adhesives, which are slidably mounted in a recloseable tube and which leave behind a tacky film when rubbed onto a receiving surface, have become part of everyday life. They contain in particular (cf. DE-PS 18 11 466) water-soluble or water-dispersible synthetic high polymers of adhesive character, particularly polyvinyl pyrrolidone (PVP) dissolved in an aqueous organic liquid phase together with a gel-forming component. The gel-forming components used include, in particular alkali or ammonium salts of aliphatic carboxylic acids, particularly those containing from about 12 to 22 carbon atoms. If the basically highly tacky aqueous preparations of the polymers of adhesive character are heated to relatively high temperatures, particularly above 60.degree. C., together with small quantities of the gel-forming component and if the solution is then allowed to cool at rest, the mixture solidifies into a more or less stiff soap gel in which the stiffening and comparatively rigid micelle structure of these soap gels is initially apparent to a predominant degree. This enables compositions of the type in question to be formed and handled in stick form in recloseable tubes. When rubbed onto a receiving surface, the micelle structure is destroyed so that the rigid composition is converted into a paste in which the adhesive character of the mixture then predominates.
2. Discussion of Related Art
Numerous attempts have been made to modify adhesive sticks of this type by modifying the gel-forming component and/or by modifying the solvent-activated adhesive-forming component. DE-AS 22 04 482 uses the reaction product of sorbitol and benzaldehyde as gel-forming component. According to DE-OS 26 20 721, salts of substituted terephthalic acid amides are used as gelling agents. According to DE-OS 20 54 503, free long-chain aliphatic acids or esters thereof rather than alkali metal salts of aliphatic carboxylic acids are said to represent the gel-forming component. DE-OS 22 19 697 seeks to improve adhesive sticks of the type in question by incorporating anionic, non-soapy wetting agents in the stick, particularly with a view to improving its rubbing on the substrate. According to DE-OS 24 19 067, a reaction product of aromatic diisocyanates with mono- and/or dialkanolamines is said to be used as the gel-forming component.
Despite all these proposals, the oldest form of adhesive sticks of the type in question here based on soap gels, which are described in DE-PS 18 11 466 cited at the beginning, remains by far the most widely used. A solution of PVP in an aqueous organic solvent mixture is converted into the form of the soft-rubbing adhesive stick by incorporation of alkali soaps of aliphatic carboxylic acids.
German patent application DE 36 06 382 describes an improved adhesive stick which additionally contains a limited quantity of lactams of lower aminocarboxylic acids and/or the corresponding ring-opened aminocarboxylic acids to improve its soft rubbing characteristics.
Although the adhesive sticks mentioned above have sufficient strength for glueing paper, there is still a need for adhesive sticks which can be universally used and with which relatively high-strength glueing can be carried out. More particularly, the glueing of paper with the sticks should not deteriorate under adverse climatic conditions.
Another disadvantage of known adhesive sticks is that, before formation of the soap gel, the stick composition is highly viscous in the heated state which results in bubble formation and also complicates processing in other respects.